What Type Of Gravel Goes Under Concrete?

How deep should Gravel be under concrete?

Excavate the slab area to a depth of about 7 inches, allowing 3 inches for a gravel base and 4 inches for concrete..

Is sand a good base for concrete?

Pour concrete over a solid, well-drained base Because concrete slabs “float” on the soil, soft ground or voids underneath may cause unsupported areas to crack under heavy weight like vehicles. … of sand or gravel over clay and other poorly draining soils to provide even support.

Can I pour concrete over old concrete?

Yes, you may pour a concrete pad overlay over an existing slab. You need to consider the added height and weight of the overlay on the existing structure. Overlays may include polymers, portland cement concrete, or epoxies. … You should improve the drainage of the slab by having a good slope on the overlay.

Can you pour concrete over pea gravel?

A slab with living area over it usually has a gravel bed to facilitate drainage. It should be ok to pour concrete over your gravel walk although you might want to give the concrete a little more depth along the sides. you might want to give the concrete a little more depth along the sides.

What kind of gravel do you put under concrete?

Backfill beneath concrete flat-work along foundation walls should be accomplished with a granular material that is uniform in size. Some fill materials, such as round stones like pea gravel, tend to be self compacting. “I recommend open-graded granular material be used,” says Tull.

What is the best base for concrete slab?

Most concrete contractors want a mix of coarse and fine aggregate to create a compactable base that is going to be safe for settlement and drainage. Crusher run (a mix of crushed stone and stone dust) is one of the best base materials for concrete flatwork.

Why do they put plastic under concrete?

The sand layer cannot dry downwards by vapor diffusion because of the plastic sheet—it is a vapor barrier after all. In fact that’s why we have it under the slab. … ** We want to prevent water vapor from coming up from the ground into the concrete slab.

Do I need plastic under concrete?

A concrete vapor barrier is any material that prevents moisture from entering a concrete slab. Vapor barriers are used because while fresh concrete is poured wet, it’s not supposed to stay that way. It needs to dry and then stay dry to avoid flooring problems. … This is why a vapor barrier under concrete is essential.

What size gravel is best for concrete?

The usual range employed is between 9.5mm and 37.5mm in diameter. – Fine aggregates are usually sand or crushed stone that are less than 9.55mm in diameter. Typically the most common size of aggregate used in construction is 20mm. A larger size, 40mm, is more common in mass concrete.

How do you prepare the ground before pouring concrete?

Preparation is the most important aspect of pouring a concrete slab.Dig the ground down to the proper depth. … Smooth out the ground with the flat side of a rake so that you have a level surface. … Tamp the ground with a hand tamper or mechanical tamper. … Pour 2 inches of small, rounded gravel for additional drainage needs.

What can I use for base under concrete?

Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.

Is gravel needed under concrete?

Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel is especially important in clay soil because it doesn’t drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains.

Can I pour concrete directly on dirt?

A good base is everything! You may be able to pour directly over sandy or gravelly soil without bringing in any additional base. But if you live in a cold climate, are pouring over heavy clay or organic soil, or plan to park heavy vehicles on the driveway, you may want to increase the base layer to 10 or 12 inches.

Is wire mesh better than rebar?

Support: Considering the support constraint, rebar is undoubtedly stronger than wire mesh. Several constructors consider rebar for domestic jobs. For thicker driveways and locations that involve greater traffic, rebar is always a good option to consider.

Should you put plastic under concrete driveway?

Never place concrete directly on a polyethylene vapor barrier or bone-dry subgrade. The subgrade should be damp, with no standing water. Polyethylene vapor barriers do not allow for proper drainage of the excess water in the mix, forcing all of the water to rise to the top. … The water to cement ratio should not exceed .

Do you need rebar for 4 inch slab?

No, depending on your proposed loads. But a 4″ thick slab really shouldn’t have rebar in it, too thin. Most thing slabs, like driveways or sidewalks have a wire mesh reinforcement in them not rebar. 6x6x10/10 mesh is typical.